Cam driven rotary index drives are employed to repeatedly move objects from one position to another position while achieving better accuracy, higher load capacity, and lower maintenance as compared with more conventional methods of manipulating an object's position, such as the pawl and ratchet. Cam driven rotary index drives typically include an indexer output mounting plate connected to a machine component which is to be indexed in rotary increments. The indexer output mounting plate includes several cam followers arranged in a circular array in order to cooperate with one or more cam tracks of an adjacent precision cam as the cam is rotated. The cam tracks are configured to impart a predetermined rotary indexing motion to the indexer output mounting plate via interaction with the cam followers as the cam is rotated.
A cam follower typically includes a cylindrical mounting shaft having a rotatable cam follower shell or member supported by anti-friction bearings on one end of the shaft for engaging the cam track. One conventional method of securing the cam follower to an indexer output mounting plate is to provide external threads on the end of the mounting shaft opposite the rotatable cam follower shell, and fastening the mounting shaft in an internally threaded bore in the mounting plate. Another conventional method would be to attach a locking nut onto the external threads of the cam follower mounting shaft and screw down until the locking nut meets the indexer output mounting plate surface.
This method suffered from a serious shortcoming, in that the face of the locking nut is generally not perfectly perpendicular to the axis of the cam follower mounting shaft. As a result, tightening of the locking nut tends to undesirably bend the cam follower mounting shaft, making it difficult for the cam follower wheel to ride squarely within an associated cam track. In order to overcome this problem, it is necessary to go to additional time and expense to machine down the face of the locking nut.
An alternate known method for securing a cam follower to an indexer output mounting plate disclosed in U.S. Pat. No. 5,724,861, utilizes an internally threaded bore within the mounting shaft at the end of the mounting shaft opposite the rotatable cam follower shell. An externally-threaded mounting screw extends through the indexer output mounting plate, and is threadably received in the threaded bore of the cam follower mounting shaft. A washer is disposed between the screw and the end of the cam follower mounting shaft having the internally threaded bore.
Although these various methods may be suitable for securing average-sized cam and larger followers in mounting plates, there are still several shortcomings associated with them. First, the rotation of the cam causes a reversing axial force on the cam follower that tends to pull the cam follower out from the bore in the mounting plate, or push the cam follower too far into the bore in the mounting plate. This axial force can be a result of misalignment of the cam to the follower, relative slip of the follower to the cam track, or lack of perpendicularity of the cam track itself. Although the methods mentioned above do provide some means of distributing such forces, it would be desirable to have a more effective way to prevent premature dislodging of a cam follower from a mounting plate. Also, neither internally nor externally thread mounting shafts are practicable with small-sized cam followers. Machining of threads to tight tolerances becomes more difficult and, in cases of particularly small cam followers, cost prohibitive.
An additional shortcoming of prior art cam followers is the cost associated with the material required for the relatively long stud shaft section and relatively large nut portion. It would be beneficial to provide a secure mounting assembly for cam followers that do not have such large, costly material requirements.
Cam followers are measured in units of inches, and a typical follower size is about 2 inches in diameter, with a length of about 3 inches. However, smaller-sized cam followers, such as generally ranging from about 1 inch diameter, down to about 0.276 inch diameter, are more suitable for certain cam index drive systems, such as index drive systems used for electronic production systems, or inspection/quality control systems. It would further be desirable to have a reliable way to secure such small-sized cam followers in their respective output mounting plates.